When you feel yourself getting angry, just ask yourself “does this issue REALLY matter”.
If it really matters then by god get angry. If it doesn’t matter then why bother?
I rarely if ever got angry again after I started asking myself this, cause not much actually matters.
Sometimes it's actually frustration that things aren't going the way you want (and the next question is why is my way really better than the other?).
Sometimes it's someone else's mistake (and the next question is have I ever made a mistake?)
Then someone cuts in front of you in line and it could really matter (time pressure or opportunities missed) and that behaviour could be something you would never do to others. In that situation believe it's healthier to speak up, but there is much less risk of escalation, and a good chance of gaining allies around you if the message is delivered calmly rather than with anger.